1. Field of the Invention
The present invention relates to a developing machine for developing an electrostatic latent image which is formed on a photosensitive drum, and more particularly to the toner distribution mechanism of a developing machine.
2. Description of the Related Art
In an electrophotographic developing machine, a developing agent in which a non-magnetic toner is mixed with a carrier has been used. More recently, a new developing agent in which a magnetic toner is mixed with a carrier has been used. Generally, a developing method employing a magnetic brush is used with the above two developing agents. In this case, the toner and the carrier are agitated with each other and are charged with electricity, whereby the toner is charged with a negative charge and the carrier is charged with a positive charge. The toner, having a negative charge, forms a shape of the brush with the carrier by the magnetic force of a magnetic roller which is mounted in a developing roller and is returned by a rotation of the developing roller and then develops an electrostatic latent image on a photosensitive drum. In this process, in order to control the thickness of the developing agent layer, a doctor blade is used.
In order to obtain a high picture quality in the above developing machine, it is important to maintain uniformly the toner concentration on the developing roller. To this end, a proper amount of developing agent should be always stored in a developing part of the developing machine. When the developing roller is idled without consumption of the developing agent, the developing agent should be not removed to the outside. In addition, when the developing agent is only partially consumed due to the particular sizes of the images, there should be provided a mechanism for returning the developing agent at a border between the developing part and a toner supplying part so that the developing agent is supplied only to the consumed area.
A conventional developing machine has a housing, a photosensitive drum on which an image is formed, a developing agent formed of magnetic particles having a diameter of 40-100 .mu.m, magnetic toner having a diameter of 10-20 .mu.m, a developing roller having an axis and a magnetic roller which is disposed in the developing roller and composed of alternating magnets N1, S1, N2, S2, N3, S3. The developing agent is composed of ferrite or magnetite.
Additionally, the conventional developing machine has a doctor blade for controlling the thickness of the developing agent layer, a toner supplying roller for supplying the magnetic toner to the developing roller and a rib for preventing a movement of the developing agent. The rib is mounted on a portion in which the developing agent remains. The rib is fixed on a frame by a screw. Further, the rib controls movement of the developing agent in the axial direction of the developing roller.
In another conventional developing machine, a rib is integrally projected from the rear face of a doctor blade. However, in both discussed conventional developing machines, the ribs are provided only to prevent the axial movement of the developing agent, due to vibration and inclination of the developing machine or pressure of the magnetic toner which is returned.
Therefore, as described above, when the developing roller is idled without consumption of the developing agent, the ribs prevent the axial movement of the developing agent, due to vibration and inclination of the developing machine. However, when actually printing an image, since there is a large difference between the input amount of the developing agent at the front of the doctor blade and the output amount at the rear of the doctor blade, the developing agent which is not output flows intensively. The developing agent flows down along the ribs. Therefore, a portion of the developing agent secedes from the developing part to the toner supplying part, and an imbalance of the concentration of toner is generated on the developing roller.